Donald Trump ran away with South Carolina on Saturday night. Coming on the heels of his 20-point victory in New Hampshire, it’s official: The candidate everyone dismissed back in June has significant momentum heading into Nevada on Tuesday and then Super Tuesday on March 1.

So, does that make him a shoo-in for the nomination, or can he be stopped?

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Politico Magazine asked top political insiders to tell us whether Trump is really the inevitable GOP nominee—and if not, how the Republican establishment can stop him. Many said the answer is Marco Rubio—but only if John Kasich steps aside in time and Rubio de-automates his debate performances. Others were not about to underestimate the GOP front-runner again. Trump is “like a rolling bowling ball knocking Ted Cruz and everyone else to the side,” one strategist said. Another put it more starkly: “The only question that the GOP faces is pretty simple: Whom will Donald Trump choose for vice president?”

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‘It’s now Trump’s party’Jacob Heilbrunn, editor of the National Interest and author of They Knew They Were Right: The Rise of the Neocons

The last time Ohio’s Cuyahoga River caught on fire was in June 1969. This summer it might burst into flame again—not because of an oil slick but because of the sparks that will be flying at the Republican convention in Cleveland. To the anguish and fury of the Republican nomenklatura, the GOP will nominate a candidate who has with impunity violated pretty much every tenet of conservative political correctness, whether it was his disavowal of a crusading foreign policy or his support of a universal healthcare mandate.

With Donald Trump’s crushing win, South Carolina, you could say, has become the graveyard of the establishment. There will be no Marco Rubio or Jeb Bush to restore the old orthodoxies. No House Speaker Paul Ryan to emerge at a brokered convention as the GOP’s savior. No jejune talk about modern conservatism resembling a “Benetton Commercial.” Instead, the only question that the GOP faces is pretty simple: Whom will Donald Trump choose for vice president? It surely won’t be Nikki Haley. In fact, don’t expect him to look to the establishment for an answer to this—or any other—question because he owes it nothing except payback. It’s now Trump’s party.

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‘March 15 will be the key date’Howard Dean, former governor of Vermont, chairm of the Democratic National Committee and 2004 Democratic presidential candidate

Donald Trump is close to clinching, but with Jeb Bush out, this gets tougher for him. March 15 will be the key date. It’s the first winner-take-all day, and Florida is up with only one Floridian still in the race.

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‘He can be beaten if candidates forget about winning their “lanes”’Stuart Stevens, Republican consultant who was Mitt Romney’s chief strategist in the 2012 presidential campaign

Donald Trump has now won nine fewer primaries than Rick Santorum did in 2012. He can be beaten if candidates forget about winning their “lanes”—there are no lanes—and focus on winning states. It takes concentrated, sustained focus contrast every day.

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‘Trump can absolutely be stopped’Bill Scher, senior writer at the Campaign for America’s Future, co-host of the Bloggingheads.tv show “The DMZ” and a contributing editor at Politico Magazine

Donald Trump can absolutely be stopped, by rallying the party’s anti-Trump voters around a single figure. Give Marco Rubio the Jeb Bush and John Kasich voters in South Carolina, and he would have beaten Trump by five points.

Trump has scored in the mid-30s for his two victories. He may not have reached his absolute ceiling, but he can’t count on peeling off support from the remaining anti-establishment candidates. Ted Cruz’s libertarians and Christian conservatives, not to mention Ben Carson’s, won’t organically drift into Trump’s more authoritarian camp. A full court press behind Rubio should be able to get him over 35 percent.

And with Hillary Clinton’s hold on the Democratic nomination now firmer, it will be easier for Rubio to get Republican voters to focus on electability. Rubio can say, accurately, that polls show him beating Clinton and Trump losing.

But one thing Rubio has to do, that he hasn’t had to yet, is face down Trump in a debate. For his sake, hopefully he’s learned something after being mauled by Chris Christie.

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‘It is Trump who now stands between the nomination and all other comers’Beth Myers, Republican political consultant and lawyer, and former adviser to Mitt Romney

Inevitable, no. Only three states have voted. But Trump clearly is now the front-runner for the Republican nomination, both in delegate count and momentum. Some may characterize him as a weak front-runner with damaging vulnerabilities: Trump has yet to demonstrate that he can push past a 35 percent vote ceiling, and that matters more as the geometry of the race changes with the exits of Jeb Bush and Chris Christie. Trump has never been the subject of a focused, tough and prolonged paid media attack by any of his adversaries or a super PAC. The virtual second place tie in South Carolina leaves Marco Rubio and Ted Cruz, two strong and able contestants, still ready for action on the playing field. And Nevada’s caucuses, the March 1 SEC primaries and the winner-take-all contests on March 15 will undoubtedly yield victories for these candidates.

But despite all this, it is Trump who has dominated and defined the contours of the Republican race in 2016, and it is Trump who now stands between the nomination and all other comers.

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‘No one will stop him now—except himself’Robert M. Shrum, professor of the practice of political science at University of Southern California and a former Democratic strategist, speechwriter and media consultant.

Donald Trump is not a lock now, of course—but he is irrepressible and maybe inevitable, despite the Politico Caucus’ tendency to convert wishes into analysis. Trump speaks to the alienation, anger and reaction of a wide swath of the base. No one will stop him now—except himself. But so far, as hard as he’s tried, he hasn’t trumped Trump.

The GOP establishment will gather against him. But it appears poised to be crushed—before resigning itself to Trump. That will please Democrats. Jeb Bush is gone now, and Democrats are rooting for anybody but Marco Rubio. From a Democratic perspective, I would endorse Trump as a likely November loser, but my first choice for the GOP is actually Ted Cruz, an extremist more likely than Trump to lose, lose, lose.

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‘There is room for a challenger to consolidate past him’Brent Colburn, fellow at the Harvard Institute of Politics, former assistant to the secretary of defense for public affairs and national communications director for Barack Obama’s 2012 campaign

24. 35. 33. Remember these numbers. With a little rounding, they are the vote percentages for Donald Trump in Iowa, New Hampshire and South Carolina. If you look at the GOP field, it’s clear that you’d rather be Trump than any of his opponents right now. But if you take a step back and look at the numbers, it’s also clear that Trump has still not answered the question at the heart of his candidacy: Can he get substantially more than a third of GOP primary voters to show up and pull the lever for him? The answer might end up being yes, but so far there isn’t any evidence that it is. If Trump can’t start getting his numbers consistently above 40 percent in the upcoming states (especially after the buzz coming off of two wins, in New Hampshire and South Carolina), then there is room for a challenger to consolidate past him. If he keeps putting up the same numbers he has, his rivals don’t even have to peel off Trump voters to catch him. And, more importantly, if he continues to hover in the thirties, it does not bode well for him in a general election. Winning crowded primaries is better than losing crowded primaries—but it’s hard to ride one-third of one party to the White House.

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‘Rubio … desperately needs John Kasich to drop out’Ron Bonjean, Republican strategist and a founding partner of the public affairs firm Rokk Solutions

The clock is now ticking faster against establishment Republicans as Donald Trump begins to knock down the early primary states. With his win in South Carolina, Trump is quickly building solid momentum like a rolling bowling ball running fast down the lane, once again knocking Ted Cruz and everyone else to the side. The stakes are also getting higher, and Jeb Bush made the right decision to drop out for the good of the establishment wing of the party. We will likely see the floodgate of donors and grassroots support now shift over from Bush to Marco Rubio. However, if Rubio is going to have a good shot at taking any of these upcoming states, he also desperately needs John Kasich to drop out to further consolidate the field. It remains an open question whether Trump can be stopped in his tracks. If the past is prologue, that could be tough to accomplish. But the race is growing deadly serious, and Kasich needs to make a tough decision imminently.

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‘The front-runner … but not his party’s inevitable nominee’Anita Dunn, Democratic political strategist and White House communications director from April-November 2009

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Donald Trump leaves South Carolina the front-runner for his party’s nomination, but not his party’s inevitable nominee. With Marco Rubio’s narrow second place victory in South Carolina, Jeb Bush’s departure from the race and the continued great winnowing of the field (who else is nostalgic for the undercard debates?), Trump is going to be in a smaller field. That is a different race, given the strength of his unfavorable ratings in his own party. The question is how quickly the Republican race gets to a two-person contest, and is the second person Rubio? That is a scenario in which Trump probably isn’t as inevitable as he appears this morning.

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Rubio has the ‘financial and political space to begin consolidating the mainstream conservative movement’Rick Wilson, a national Republican message and media strategist (who has made ads for a Marco Rubio super PAC)

Donald Trump’s victory in South Carolina isn’t the story of the night. The real story is that Jeb Bush has left the race, giving Marco Rubio financial and political space to begin consolidating the mainstream conservative movement—and focusing on the destruction of Donald Trump. Rubio is clearly the most electable candidate against the unlikable Hillary Clinton because he’s an optimistic, likable candidate of the mainstream conservative movement without Ted Cruz’s oleaginous affect or Trump’s lunatic bluster.

The Bush super PAC Right to Rise will also no longer be pummeling Rubio with millions in negative TV ads as they did in Iowa, New Hampshire and South Carolina. No other campaign or PAC had the resources to nuke Rubio like Right to Rise did, and with them off the playing field, Rubio’s positives will move up swiftly. Finally, the attacks on Rubio’s immigration record by Trump, Cruz and their pet media outlets (Mark, Levin, Trumpbart News, Conservative Review, et al.) failed in South Carolina, a state that should have made those attacks utterly toxic to Rubio’s campaign. They’ll keep trying, but the anti-Rubio immigration attack was proven to fail in a place it should have succeeded. That bodes well for Rubio, and not Trump.